Den Fri, 15 Jun 2018 16:11:02 +0200 skrev Michał Pleban <lists@michau.name>: > Hello! > > Marko Mäkelä wrote: > > > These functions are fairly independent of each other. Would it be > > feasible to implement the CIA in two CPLDs that would share the > > address and data bus interface? > > Theoretically it should be possible. Some functions would be > duplicated (like register decoding etc) but it might be doable. The register map is unfortunitely made in a way that it won't be a great idea to split it so one CPLD handle the odd addresses and the other the even addresses. 0000 data port A 0001 data port B 0010 DDR A 0011 DDR B 0100 Timer A low byte 0101 Timer A high byte 0110 Timer B low byte 0111 Timer B high byte 1000 TOD 1/10s BCD 1001 TOD seconds BCD 1010 TOD minutes BCD 1011 TOD hours 1100 serial shift register 1101 Interrupt control and status 1110 Timer A control 1111 Timer B control Maybe it would be easiest to implement data port A in one CPLD and the rest in another? Afaik data port A doesn't have any dependencies on the other parts of the CIA except address decoding, while everything else has some kind of dependences. http://archive.6502.org/datasheets/mos_6526_cia_preliminary_nov_1981.pdf IMHO before someone does implement a CIA as a CPLD, the analogue electrical characteristics of the CPLD ports should be observed. The data sheet states that it can source at least 0,2mA and typically 1mA, while it can sink at least 3.2mA. It is rather important that the key decoding actually works. A device with symmetrical drive capability would be far from ideal. It might be neccesary to have two pins for each CIA port pin, one that inputs and drives outputs low, and one that solely drives output high which in fact would more or less just be connected to the other pin and the CIA replacement pin with a series resistor. Btw the 6522 data sheet lists different current drive between port A and B. Are we 100% sura that this isn't the case with the CIA's in C64? http://archive.6502.org/datasheets/mos_6522_preliminary_nov_1977.pdf -- (\_/) Copy the bunny to your mails to help (O.o) him achieve world domination. (> <) Come join the dark side. /_|_\ We have cookies.Received on 2018-06-16 06:00:04
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